The parasympathetic ganglion in the heart of frogs will be used to investigate the cellular basis for the regeneration of damaged axons and the specificity of synapse formation during reinnervation. Because the ganglion is embedded in a thin tissue and individual parasympathetic neurons can be seen in the living isolated tissue, this allows us to correlate data from intracellular recordings with light and electron microscopy on single identified neurons. We will also utilize high voltage electron microscopy to reconstruct single neurons from serial semi-thin sections. I propose to investigate the striking reorganization of synaptic connections occurring in the cardiac ganglion when some but not all of the preganglionic endings are destroyed by partial denervation. We will study intracellular synaptic responses from newly formed sprouted synapses, using online computer analysis to investigate the details of these responses. We will investigate whether regeneration of the damaged axons after partial and after complete denervation will restore the former pattern of ganglionic synapses. Lastly, we will test whether denervated parasympathetic neurons in the cardiac ganglion will form functional synapses with somatic motor axons, to test further the specificity of synapse formation after damage in nervous tissue. These results will be important not only for understansing how the vertebrate cardiac ganglion regulates the heart rate, but can contribute fundamental information relating to what factors are important for restoring synaptic connections after damage in the nervous system in general.